MZ 250 ETZ - start problem

[matzika]

Hi,

I have an ETZ 250 which currently has a weird issue when trying to start it up when the fuel is open. When the engine is cold, the motorbike starts from the first try and runs smoothly, but when the engine gets warm (not sure if that's even relevant), and the fuel is left open, you cannot start it. The only way to start the engine is to close the fuel, then after 2-3 kicks, the engine will start, and open the fuel back.

I have a PWK 30 carburettor with 40 slow pilot jet, 105 main jet and the mixture screw is ~1 full circle opened. The fuel level and the float are configured correctly, and everything seems okay. The carburettor doesn't leak anywhere, neither from the outside or inside. The float is also not getting stuck, so it's not letting too much fuel through. The engine has been rebuilt and everything is in great shape. The ignition is fully electronic AudioBas for ETZ.

The only thing only thing that currently is on my mind (and that's a long shot) is that the pressure from the tank and in the fuel hose is pretty high, and it's causing the float to open and push a little bit more of fuel, causing the engine being unable to start because of too much fuel in the system.

Any other ideas?

Thanks.

[Blurredman]

Do you think perhaps the float is not 'floating' ? Have you checked by chucking it in a bowl of water etc?

[breakwellmz]

Hi,

I have an ETZ 250 which currently has a weird issue when trying to start it up when the fuel is open. When the engine is cold, the motorbike starts from the first try and runs smoothly, but when the engine gets warm (not sure if that's even relevant), and the fuel is left open, you cannot start it. The only way to start the engine is to close the fuel, then after 2-3 kicks, the engine will start, and open the fuel back.

I have a PWK 30 carburettor with 40 slow pilot jet, 105 main jet and the mixture screw is ~1 full circle opened. The fuel level and the float are configured correctly, and everything seems okay. The carburettor doesn't leak anywhere, neither from the outside or inside. The float is also not getting stuck, so it's not letting too much fuel through. The engine has been rebuilt and everything is in great shape. The ignition is fully electronic AudioBas for ETZ.

The only thing only thing that currently is on my mind (and that's a long shot) is that the pressure from the tank and in the fuel hose is pretty high, and it's causing the float to open and push a little bit more of fuel, causing the engine being unable to start because of too much fuel in the system.

Any other ideas?

Thanks.

The tank is vented via the filler cap (Or should be!) So, even when left in the sun on a hot day the tank won`t pressurise.
Does it smoke a lot when it does re-start?

[matzika]

Do you think perhaps the float is not 'floating' ? Have you checked by chucking it in a bowl of water etc?

I have checked the float, and it's floating properly, and closing the fuel properly. Sank it in the bowl of water, and tried to blow into the hose, and the fuel was closed as it was supposed to be.

The tank is vented via the filler cap (Or should be!) So, even when left in the sun on a hot day the tank won`t pressurise.
Does it smoke a lot when it does re-start?

It does smoke a lot indeed. The symptoms are really that the carburettor is not closing the fuel properly (but I have re-checked the float and it's totally fine), and it would start only if I close the fuel and kick it again a few times. If you don't close the fuel and manage to start it up, you can't rev it up because there's too much fuel in the system and a lot of smoke.

[Blurredman]

Are you trying to start with choke or without?

I wonder, I know it's not a resolution but don't you turn the tap off when parked anyway? I always do, just incase of leakage, both with possible line degredation but also carb overflowing perhaps.

My car (carburettored) starts right up when cold, but takes a lot of cranking to start when it is already warm- smells of petrol too. Does yours smell of petrol?

Have you got the original BVF carb? Is it worth trying that? Out of interest the PWK30 has other features that supply petrol doesn't it? I heard something about a compensation tube, if that's the right term- or maybe an accelerator pump? Could these be disabled if they are indeed on such a carb?